There is a known printing apparatus for carrying out a printing while moving a ribbon shaped ink film and a ribbon shaped film to be transferred for transfer printing ink of the ink film between a supply bobbin and a winding bobbin around which they are wound respectively, and one example of such a printing apparatus is disclosed in Japanese Patent No. 4,337,582.
In the printing apparatus as disclosed in Japanese Patent No. 4,337,582, an ink film on which ink layers of four colors are repeatedly applied in a ribbon direction and a film to be transferred (referred to as an intermediate recording medium in Japanese Patent No. 4,337,582) are moved while being in pressed contact. This pressed contact moving is repeatedly carried out with respect to an identical transfer region (transfer frame) of the film to be transferred, for each one of the ink layers of four colors. In each moving, the ink has a temperature raised by a thermal head, and the ink is transferred by sublimation or melting to the transfer frame in a pattern according to an image to be printed. In this way, a desired color image is formed on the film to be transferred.
More specifically, the color image is formed by superposed transfers of the ink of respective colors to an identical transfer frame one color by one color as the thermal head is put in pressed contact with a face on opposite side of the ink layer, while moving the ink film in a ribbon direction with its ink layer overlapping with the film to be transferred.
Namely, each time the transfer of each color is to be carried out, operations of separating the thermal head, winding and cueing one transfer frame part of the film to be transferred, cueing a next color of the ink film, and putting the thermal head into pressed contact are carried out.
Consequently, in order to form the color image using the ink of four colors, a cueing operation is carried out four times (a winding operation is carried out three times), for the film to be transferred.
In this printing apparatus, the ink film and the film to be transferred are wound around and stretched between a pair of bobbins comprising a supply bobbin and a winding bobbin that are attached to the printing apparatus in correspondence to respective films.
Then, by driving a total of four motors provided in correspondence to respective bobbins, the ink film and the film to be transferred are made to move in a feeding out and winding direction between respective pairs of bobbins.
Also, the printing apparatus as disclosed in Japanese Patent No. 4,337,582 has a re-transfer unit for transferring again the image that has been transfer printed on the film to be transferred to an object to be re-transferred (a card in this example).
For the printing apparatus, there is a demand from the market that it should be capable of realizing a high quality printing at low cost.
The printing apparatus as disclosed in Japanese Patent No. 4,337,582 has four motors, so that the dynamic characteristics in the movement of the ink film and the film to be transferred (also referred to as the transfer film) between bobbins are prone to be unbalanced, in the case where the initial fluctuations of the dynamic characteristics of respective motors are large, or in the case where the levels of change in time of the dynamic characteristics are largely different from each other.
When the dynamic characteristics are unbalanced, in the movement of the ink film and the film to be transferred (or the transfer film) between bobbins, tensions generated according to rotational torques of the supply bobbin and the winding bobbin are becoming insufficient so that there is a concern for the occurrence of troubles, such as slacking of the films occurs, a positioning in high precision cannot be made, the films are stuck together by electrostatic force, etc.
For these reasons, the printing apparatus as disclosed in Japanese Patent No. 4,337,582 requires to select motors of the relatively high cost in which the initial dynamic characteristics and their change in time characteristics are equalized.
Moreover, there has been a need to implement a control unit of high control performance that can independently control the driving of four motors simultaneously in high precision.
For this reason, it has not been easy to make the high quality printing and the low cost compatible, and there has been a room for the improvement.